Denque virus - infected mosquito cell cultures when maintained under certain conditions show no apparent cell damage, produce no incomplete virus but large amounts of infectious virus, and the progeny virus exhibit host cell modification of surface antigens (J. Virol. 12:275, 1973). Aedes albopictus cell cultures will be first rigorously examined for adventitious agents and the normal hemagglutinin produced by these cells will be characterized. These cultures will then be tested for susceptibility to infection by various arboviruses, whether the products of infection include both incomplete and complete virus and whether non-cytopathogenic infections can be established. Complete virus will be used for antigenic analysis to determine whether viruses other than dengue are modified by replication in invertebrate cells, and to determine the polypeptide composition of these viruses by polyacrilamide gel electrophoresis. Our unpublished observations indicate that dengue virus produced in albopictus cells contains four structural proteins in contrast to three proteins after maturation in vertebrate cells. Further studies will attempt to confirm the apparent cellular origin of this fourth protein, and whether this extends to other group B, or other arboviruses. The effect of immunizing suitable animals to mosquito cell proteins on the animal's susceptibility to arboviruses derived from mosquito cells will also be determined.